Patent Document 1 discloses a so-called tumble port shape as one example of an intake port structure of an internal combustion engine. Specifically, in Patent Document 1, when an intake valve opens, a downstream end portion of an intake port extends to direct to between a shade back of the intake valve positioned on the inside of a combustion chamber with respect to a valve stem and a ceiling surface of the combustion chamber facing the shade back. With this configuration, when intake air flows into the combustion chamber, the intensity of a tumble flow, particularly a positive tumble flow, generated by the intake air can be increased.